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Transcript
Cell Transport 1 Photograph of a Cell Membrane 2 Cell Membrane (or plasma) The cell membrane is flexible and allows a unicellular organism to move. 3 Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by plasma membrane controlling what enters & leaves the cell 4 Functions of Plasma Membrane Protective barrier Regulate transport in & out of cell (selectively permeable) Allow cell recognition Provide anchoring sites for filaments of cytoskeleton 5 Functions of Plasma Membrane Provide a binding site for enzymes Interlocking surfaces bind cells together (junctions) Contains the cytoplasm (fluid in cell) 6 Structure of the Cell Membrane 7 Cell Membrane Components * Phospholipids * Proteins (peripheral and integral) * Carbohydrates (glucose) * Cholesterol 8 Phospholipids • Make up the cell membrane • Contain 2 fatty acid chains that are nonpolar • Head is polar & contains a –PO4 group 9 10 • Polar heads are hydrophilic-“water loving” • Nonpolar tails are hydrophobic-“water fearing” • Makes membrane “Selective” in what crosses Hydrophobic molecules pass easily (O2, CO2, H2O); hydrophillic DO NOT (protein). 11 Solubility • Materials that are soluble in lipids can pass through the cell membrane easily. 12 Types of Transport Across Cell Membranes 13 A. PASSIVE TRANSPORT 14 1. Simple Diffusion • Requires NO energy • Molecules move from area of HIGH to LOW concentration 15 Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY. 16 Diffusion of Liquids 17 Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW). 18 2. Osmosis • Diffusion of water across a membrane. • Moves from HIGH water potential (low solute) to LOW water potential (high solute). Diffusion across a membrane Semipermeable membrane 19 Diffusion of H2O Across A Membrane High H2O potential Low solute concentration Low H2O potential 20 High solute concentration Cell in Isotonic Solution 10% NaCL 90% H2O ENVIRONMENT CELL 10% NaCL 90% H2O NO NET MOVEMENT What is the direction of water movement? equilibrium The cell is at _______________. 21 Cell in Hypotonic Solution 10% NaCL 90% H2O CELL 20% NaCL 80% H2O What is the direction of water movement? 22 Cell in Hypertonic Solution 15% NaCL 85% H2O ENVIRONMENT CELL 5% NaCL 95% H2O What is the direction of water movement? 23 Cells in Solutions 24 Isotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS 25 Cytolysis & Plasmolysis Cytolysis Plasmolysis 26 Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic 27 hypotonic hypertonic hypertonic isotonic isotonic hypotonic 28 3. Facilitated diffusion Doesn’t require energy Uses transport proteins to move high to low concentration Examples: Glucose or amino acids moving from blood into a cell. 29 Proteins Are Critical to Membrane Function 30 Types of Transport Proteins • Channel proteins are embedded in the cell membrane & have a pore for materials to cross • Carrier proteins can change shape to move material from one side of the membrane to the other 31 • Some Carrier proteins do not extend through the membrane. • They bond and drag molecules through the lipid bilayer and release them on the opposite side. 32 Carrier Proteins • Other carrier proteins change shape to move materials across the cell membrane 33 B. ACTIVE TRANSPORT 34 Requires energy or ATP Moves materials from LOW to HIGH concentration AGAINST concentration gradient 35 Examples: Pumping Na+ (sodium ions) out and K+ (potassium ions) in, against strong concentration gradients. Called Na+/K+ Pump 36 Sodium-Potassium Pump 3 Na+ pumped out for every 2 K+ 37 pumped in; creates a membrane potential Moving the “Big Stuff” 1. Exocytosis- moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another. 38 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane. 39 2. Endocytosis: moving things in. There are 2 types of endocytosis… 40 a. Pinocytosis Most common form of endocytosis. Takes in dissolved molecules as a vesicle 41 . • Cell forms an invagination • Materials dissolve in water to be brought into cell • Called “Cell Drinking” 42 Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue). 43 b. Phagocytosis * Used to engulf large particles such as food, bacteria, etc. into vesicles. * Called “Cell Eating” 44 Phagocytosis About to Occur 45 Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) 46